Tuesday, November 06, 2007

PNG population genetics

First some background on the populations in PNG and the surrounding area:

The island of New Guinea is interesting for studying human genetic history because it was occupied by anatomically modern humans as long as 35–40,000 years ago (Groube et al. 1986; Pavlides and Gosden 1994; Leavesley et al. 2002; Specht 2005) representing part of the first expansion of modern humans out of Africa. Melanesia (used here as geographic term comprising mainland New Guinea and surrounding islands in the north and east, also referred to as Near Oceania together with most of the Solomon islands) is inhabited today by speakers of 2 kinds of languages. Austronesian-speaking groups have a common ancestral language, Proto-Austronesian, and mostly live on islands around New Guinea as well as on the northeast and southeast coasts of the New Guinea mainland. Non-Austronesian (=Papuan)–speaking groups lack a (recent) common ancestry and include numerous linguistically unrelated groups. Papuan speakers dominate the New Guinea mainland, living inland from Austronesian speakers where such are present, and are also found in a few places around the islands north, northeast, and east of mainland New Guinea where their languages have persisted to modern times (Wurm and Hattori 1981; Specht 2005). These 2 groups of people have a different history in Melanesia: non-Austronesian–speaking groups reflecting the ebb and flow of language that emerged out of the Pleistocene language geography, whereas Austronesian speakers arrived as migrants from East Asia not earlier than 3,500 years ago (Kirch 1997).

What is the Trans-New Guinea hypothesis?

The genetic history of the New Guinea area prior to the arrival of Austronesian speakers has only recently begun to receive attention. The Trans-New Guinea (TNG) hypothesis proposes a very large family of languages mostly spoken along the central cordillera of New Guinea and in some regions north and south of the cordillera, with outliers in the Timor area of Island Southeast Asia. The TNG hypothesis implies an expansion of people speaking TNG languages started about 6,000–7,000 (perhaps as early as 10,000) years ago in the central highlands of what is now Papua New Guinea (PNG), most likely in connection with the expansion of agriculture, and spread both eastwards and westwards (Pawley 1998; Denham et al. 2003; Pawley 2005)

What they conlcude:

It is likely that the expansion of TNG speakers starting from the highlands of what is now PNG about 6,000–7,000 (perhaps as early as 10,000) years ago, presumably in association with the expansion of agriculture, had a great impact on shaping New Guinean Y-chromosome diversity as seen today.

and

We propose that sex-biased differences in the social structure and cultural heritage of the people involved in the 2 different expansions played an important role (among other factors) in shaping the New Guinean Y-chromosome landscape.

I wish I had more time to look at this paper more closely, because it seems to highlight both the genetic and cultural aspects of population dynamics.

The island of New Guinea received part of the first human expansion out of Africa (>40,000 years ago), but its human genetic history remains poorly understood. In this study, we examined Y-chromosome diversity in 162 samples from the Bird's Head region of northwest New Guinea (NWNG) and compared the results with previously obtained data from other parts of the island. NWNG harbors a high level of cultural and linguistic diversity and is inhabited by non-Austronesian (i.e., Papuan)–speaking groups as well as harboring most of West New Guinea's (WNG) Austronesian-speaking groups. However, 97.5% of its Y-chromosomes belong to 5 haplogroups that originated in Melanesia; hence, the Y-chromosome diversity of NWNG (and, according to available data, of New Guinea as a whole) essentially reflects a local history. The remaining 2.5% belong to 2 haplogroups (O-M119 and O-M122) of East Asian origin, which were brought to New Guinea by Austronesian-speaking migrants around 3,500 years ago. Thus, the Austronesian expansion had only a small impact on shaping Y-chromosome diversity in NWNG, although the linguistic impact of this expansion to this region was much higher. In contrast, the expansion of Trans-New Guinea (TNG) speakers (non-Austronesian) starting about 6,000–10,000 years ago from the central highlands of what is now Papua New Guinea, presumably in combination with the expansion of agriculture, played a more important role in determining the Y-chromosome diversity of New Guinea. In particular, we identified 2 haplogroups (M-P34 and K-M254) as suggestive markers for the TNG expansion, whereas 2 other haplogroups (C-M38 and K-M9) most likely reflect the earlier local Y-chromosome diversity. We propose that sex-biased differences in the social structure and cultural heritage of the people involved in the Austronesian and the TNG expansions played an important role (among other factors) in shaping the New Guinean Y-chromosome landscape.